Sound moves form its source to the ear by wavelike fluctuations in air pressure, something like the crests and troughs of ocean waves. Once way to keep from hearing sound is to use ear plugs. Another way is to cancel out the sound with anti-sound. Using a noisemarker 5 controlled by a microprocessor, engineers have produced sound waves that are half a wavelength out of phase with those of the noise to be quieted-each crest is matched to a trough, and vice versa. Once the researchers have recorded the offending sound, a microprocessor calculates the amplitude and wavelength of sound that will cancel 10 out the crests and troughs of noise. It then produces an electric current that is amplified and fed to a loudspeaker, which produces anti-sound and wipes out the noise. If the anti-sound goes out of synchronization, a microphone picks up the leftover sound and sends it back to the microprocessor, which changes the phase of the anti- 15 sound just enough to cause complete silence.

The research team has concentrated on eliminating low-frequency noise from ship engines, which causes fatigue that can impair the efficiency and alertness of the crew, and may mask the warning sounds of alarm 20 and fog signals.

1. What is the main purpose of the passage?(A) To discuss a physical handicap(B) To warn about a growing danger(C) To describe the structure of the ear(D) To report on a new invention2. The passage compares sound to(A) the rising and falling of water in the ocean(B) the crests and valleys of mountain ranges(C) a flag waving in the air(D) a machine for gauging air pressure3. The passage discusses a way to deal with an offensive noise by(A) diverting people's attention from it(B) masking it with a louder noise(C) canceling it out electronically(D) removing its source4. One of the functions of the microprocessor described in the passage is to(A) produce musical sounds(B) monitor sound patterns(C) record different kinds of noise(D) increase the volume of leftover sounds5. The microprocessor described in the passage will probably be used for(A) composing music(B) repairing alarm systems(C) eliminating engine noises(D) intensifying for warning sounds6. The researcher mentioned in the passage are concerned about unwanted noise because it can(A) cause deafness(B) create hazardous working conditions(C) influence ocean waves(D) damage loudspeakers and sound equipment7. According to the passage, what group of people will probably first from the use of the microprocessor?(A) Ship's crews(B) Research engineers(C) People with insomnia(D) Engine repair teams8. A paragraph following the passage would most probably discuss(A) the nature of fog(B) a way to improve alarm systems(C) other causes of fatigue(D) other uses for the microprocessor